Torquable, low mass medical guidewire

ABSTRACT

A guidewire for use in endoscopic retrograde cholangio pancreatography (ERCP) includes a proximal section defined by a fiber rod, a tube, and a connection mechanism for attaching the tube and fiber rod together in a collinear relationship. The guidewire also includes a flexible distal section which is attached to the distal end of the tube. The distal section is comprised of a superelastic core having a radiopaque marker disposed about its distal end, and at least a portion of the distal section is enveloped by an insulative sleeve. The superelastic core may be tapered, and the fiber rod may comprise a multiplicity of fibers encapsulated in a resin.

The present application is based upon one Provisional Patent ApplicationSer. No. 60/024,443 filed Aug. 27, 1996. Applicant claims the benefit ofthe filing date of the aforesaid provisional application under 35 U.S.C.§119.

FIELD OF THE INVENTION

This invention relates to medical guidewires, and, more particularly, toa torquable, low mass medical guidewire of the type used in endoscopicretrograde cholangeo pancreatography (ERCP).

BACKGROUND OF THE INVENTION

In ERCP, an exchange guidewire is threaded through a lumen or openchannel of an endoscope and maneuvered to a designated site within apatient's passageway to serve as a guide for positioning a device whichis used to perform a procedure. The procedure may occur within thecommon bile duct, the cystic duct, the pancreatic duct, or the left orright hepatic duct. The guidewire, the medical instrument, and the areanear the papilla of vater or the pancreatic duct are illuminated by afiber optic light source within the endoscope and may be viewed throughthe endoscope or on a video monitor using a remote imaging system. Theremote imaging system assists the operator and his or her staff tocontinuously maneuver the guidewire to maintain its position in theductal anatomy in view of any unexpected endoscope position changes, tocompensate for active motility in the gastrointestinal tract, and tomaintain guidewire position during catheter exchange procedures.

Typically, the endoscope is introduced orally and maneuvered through thealimentary canal into the duodenum. The guidewire is threaded through alumen of the endoscope and manipulated by torquing, steering, pushingand pulling to cannulate the papilla and enter the common bile duct and,if necessary, any duct branching therefrom. To withstand thesemanipulations and facilitate advancement of the guidewire withoutkinking, the guidewire is typically made of a material that has ahandling characteristic which permits the operator to have a sense ofthe guidewire position without excessive recourse to fluoroscopy, and astrength characteristic that can support the advancement of a medicalinstrument thereover without the guidewire retracting from a previouslyaccessed duct.

Conventionally, guidewires have been made using stainless steel cores,superelastic alloys such as Nitinol, or combinations of the two. Nitinolis a presently preferred material because of its flexibility; however,Nitinol and other superelastic alloys are expensive and difficult toproduce. Further, superelastic alloys do not bond well to othermaterials, and, as a result, several ERCP guidewires have beenconstructed entirely of Nitinol, for example, the guidewires describedin U.S. Pat. No. 5,379,779 of Rowland et al. and in the productliterature for Microvasive's Geenan guidewire. These guidewireconstructions are not only expensive to construct, but they providelimited torque (in inch-pounds).

As for guidewire constructions which are only part superelastic, thebond between the superelastic material and the remainder of theguidewire is believed to compromise the guidewire's ability tofaithfully transmit torque (that is, cause 360° rotation of theguidewire distal end with equal rotation of the proximal end) across thebond to the guidewire distal end. Further, it has been difficult toproduce a highly torquable guidewire of simple construction usingsuperelastic alloys in conjunction with other materials.

One design which has been constructed using a superelastic distalsegment in combination with a solid core is disclosed in U.S. Pat. No.5,111,829 of de Toledo. However, the stainless steel solid core isdifficult to join with the Nitinol distal segment, and no attempt ismade to reduce the mass of the overall guidewire. Operators of suchconstructions have had difficulty in directing known guidewirespresumably due to inertial forces of the guidewire which result from thetransmission of torque to the guidewire distal end. The inertial forcetends to cause the guidewire to turn farther than desired (a phenomenaknown as "whipping") which exacerbates the problem of negotiatingtortuous passageways.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved guidewire foruse in endoscopic procedures, particularly ERCP.

It is another object of the invention to provide an exchange lengthguidewire for use in endoscopic procedures.

It is a further object to provide a highly torquable guidewire that haslow susceptibility to whipping.

According to one aspect of the invention, a guidewire for use inendoscopic retrograde cholangio pancreatography includes a proximalsection defined by a fiber rod, a tube, and a connection mechanism forattaching the tube and fiber rod together in a collinear relationship.The guidewire also includes a flexible distal section which is attachedto the distal end of the tube. The distal section is comprised of asuperelastic core having a radiopaque marker disposed about its distalend, and at least a portion of the distal section is enveloped by aninsulative sleeve. The superelastic core may be tapered, and the fiberrod may comprise a multiplicity of fibers encapsulated in a resin.

These and other features and advantages of the invention will be readilyapparent from the following detailed description of a preferredembodiment taken in conjunction with the accompanying unscaled drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic, elevational view of a guidewire threaded intoan endoscope;

FIG. 2 is a cross-sectional view of a proximal end of a guidewireaccording to the a preferred embodiment taken along line 2--2 of FIG. 1;

FIG. 3 is an elevational view, partially in cross-section, of aguidewire according to the invention;

FIG. 4 is cross-sectional view of the guidewire taken along line 4--4 ofFIG. 3;

FIG. 5 is cross-sectional view of the guidewire taken along line 5--5 ofFIG. 3;

FIG. 6 is an elevational view of a subassembly of the guidewire;

FIG. 7 is a detailed view, in cross-section, of the guidewire accordingto a modified embodiment of the invention;

FIG. 8 is a cross-sectional view of the guidewire taken along line 8--8of FIG. 3;

FIG. 9 is a graphical illustration of normalized torque transmissionverses percent of clockwise rotation of a guidewire according to theinvention; and

FIG. 10 is a graphical illustration of normalized torque transmissionverses percent of counterclockwise rotation of a guidewire according tothe invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

By way of overview and introduction, FIG. 1 illustrates an ERCPguidewire 10 having a diameter of about 18 to 35 mils inserted into anendoscope 12. Preferably, the guidewire 10 is about 450 cm long and hasa bent distal end 14. The distal end 14 may be formed as a hockey-sticktip (as shown), a J-tip, or other shape as may be desired for a givenprocedure. The guidewire 10 is advanced beyond the endoscope 12 andsteered into the patient's body passageway to a preselected duct.

Because the guidewire 10 is small compared to the operator's fingers, avice or handle 16 is selectively attached to the guidewire 10 at a pointproximal to the proximal end of the endoscope 12 (FIG. 1). Rotation ofthe comparatively wider vice 16 causes a corresponding rotation of theguidewire distal end 14 within a plane and provides the operator with asense of the degree of guidewire rotation. In other words, the vice 16facilitates torquing of the guidewire. By torquing the guidewire 10, thedistal tip 14 is directed toward the opening in a side or branchingpathway to facilitate advancement of the guidewire 10. Thecross-sectional view of FIG. 2 illustrates a plurality of (optional)flattened segments 18 which provide surfaces that are engaged byclamping action of the vice 16 to selectively yet rigidly couple thevice 16 and guidewire 10 together. The vice 16 is removed prior toadvancement or withdrawal of a catheter 11 over that portion of theguidewire, and need only be used, if at all, while steering theguidewire 10 to a designated site.

Turning now to FIGS. 3-6, the guidewire 10 according to a preferredembodiment is described. The guidewire 10 generally comprises a distalsegment 19 and a proximal segment 21. The distal segment 19 includes asuperelastic alloy core 20 (25 cm to 40 cm long), preferably Nitinol,and the proximal segment 21 includes a tubular section 22 (3 cm to 240cm long) preferably made of stainless steel, a fiber section 24 (180 cmto 220 cm long) preferably made of a glass/epoxy composite andcomprising a multiplicity of glass fibers, and an attachment (selectiveor permanent) which connects the tubular section 22 and the fibersection 24 in a collinear relationship. The alloy core 20 and the fibersection 24 each have a reduced diameter end, 26, 28, respectively, whichis shaped to be seated within a lumen 30 of the tubular section 22. Thethree elongate elements (the alloy core 20, tubular section 22, andfiber section 24) are preferably permanently attached to one another byan adhesive bond, crimping, swaging, or other conventional means. Thisarrangement provides a particularly strong union between the alloy core20 and the tubular section 22 for faithful transmission of torque. Thisis especially important when the alloy core 20 is made of a superelasticalloy because such alloys are well known to be difficult to join toother materials.

In the modified embodiment of FIG. 7, the fiber section 24 is detachablefrom the tubular section 22 and forms an extension section whenconnected. The reduced diameter end 28 of the fiber section 24 in thismodified embodiment has spiral threading 32 extending therefrom whichmay be advanced past a dimple 34 in the tubular section 22 by rotationof the fiber section 24 relative to the tubular section 22, whereby theformer is engaged to the latter. The threaded distal end 28 is shaped soas to have a maximum outside diameter which closely approximates theinside diameter of the lumen 30 of the tubular section 22. Furtherdetails of this construction are provided in U.S. Pat. No. 5,267,573 ofEvans and assigned to the present assignee, the disclosure of which ishereby incorporated by reference as if set forth fully herein.

Preferably, the guidewire 10 is jacketed in an electrically insulativecover or coating which may provide a substantially uniform outsidediameter to the guidewire 10 from the distal end 14, across the unionsof the guidewire segments 19 and 21 and toward the guidewire's proximalend. The distal segment 19 may be covered with a sleeve 36, preferablypolyurethane, chosen to be of an elasticity which matches orapproximates the elasticity of the alloy core 20.

The sleeve 36 may be a polyimide thermoset resin having steel-braiding38 impregnated therein to improve the transmission of torque to thedistal tip 14 (FIG. 4). Also, the sleeve having the steel-braiding 38may progressively decrease in stiffness from its proximal to its distalend, for example, by reducing from about 140 PICS/inch at its proximalend near the union with the tubular section 22 to about 60 PICS/inch atthe distal tip 14 to enhance the handling characteristics of theguidewire 10, especially if the alloy core 20 tapers toward the distaltip 14. A greatly preferred performance characteristic is that thesleeve 36 be formed from a material which does not deform over thesmallest bend radius likely to be encountered during a particularprocedure. The sleeve 36 may further have a radiopaque materialimpregnated therein to facilitate fluoroscopic monitoring.

Turning now to FIG. 5, the alloy core 20 is shown as having tapered froma first diameter D at a proximal portion (FIG. 4) to a second, smallerdiameter d at a distal portion. By tapering the alloy core 20, distalflexibility of the guidewire 10 is enhanced and the guidewire distal tip14 is therefore softer to better ensure an atraumatic insertion into apatient. However, there need not be any taper in the alloy core 20,especially where it is made of a superelastic material; the proximal endof the alloy core 20 may have a diameter which is no greater than thediameter of the distal end of the alloy core 20.

Also illustrated in FIG. 5 is a coil spring 40 disposed about the distal1 to 10.5 cm of the distal segment 19 (cut through a cross-section 42),and may be secured to the alloy core 20 by a liquid adhesive such asepoxy. The coil spring 40 may be made of a radiopaque material to assistin fluoroscopic monitoring of the guidewire, or may be made of stainlesssteel wire and have a segment coated with a radiopaque materialselected, for example, from the group including platinum, tantalum,tungsten, gold, tantalum oxide, and combinations thereof alone or withother elements. This latter arrangement provides a radiopaque markerwithout affecting the stiffness properties of the alloy core 20, andhence the handling characteristics of the distal end 14 of the guidewire10. The coil spring 40 may also be adapted (e.g., by suitable choice ofmaterials or by metal working) to take a set such as the hockey-sticktip shown in FIGS. 1 and 3. (Alternatively, a forming wire may besecured to the alloy core 20, coil spring 40, or sleeve 36 inconventional manner, for example, by soldering, welding, or crimping theforming wire to the distal end of the coil spring 30, melting it to thesleeve 36, adhesively bonding it to the core 20, or any combination ofthe above.)

Alternatively, spring coils made of different materials may be joinedtogether to space one or more radiolucent coil segments by one or moreradiopaque coil segments of a predetermined length, interleaved asdisclosed in U.S. Pat. No. 4,922,924 of Gambale et al. and assigned tothe present assignee, the disclosure of which is hereby incorporated byreference as if set forth in its entirety herein, stretched to havevarying pitch whereby the opacity of a radiopaque coil is modified,provided with a radiopaque polymer filler as a marker (which filler maybe thermoset within the coils of a stainless steel coil), and the like.

FIG. 6 shows the spring 40 disposed about the distal end of the alloycore 20 prior to the sleeve 36 being extruded or joined to the alloycore 20/spring coil 40 subassembly. The alloy core 20 is shown having adecreasing diameter from its proximal end to the distal end 14, forexample, as a result of taper-grounding a rod of Nitinol material.Although the coil spring 40 is shown having a generally uniformdiameter, it could be wound to match a taper in the alloy core 20, ifthere is any taper. The sleeve 36 is preferably melted to a rounded tip44 (FIG. 3) and envelopes the alloy core 20 and coil spring 40 toprovide a unitary distal segment 19 assembly for insertion into apatient.

Preferably, the tubular section 22 is made of a hyperdermic tube("hypotube"), for example, #304 stainless steel hypotube or a tubularmaterial of similar rigidity. The applicant has discovered that the lowmass of a tube as compared to a solid core reduces the inertial forcestransferred to the guidewire distal tip 14. This reduces the tendency ofthe guidewire 10 to whip while being advanced and steered to adesignated site. Thus, the rotational response characteristic (torquetransmission) from the proximal end to the distal end of the guidewireis enhanced as compared to conventional ERCP guidewires by constructingthe majority of the guidewire 10 from the tubular section 22, i.e., thehypotube.

With reference now to FIGS. 9 and 10, torque transmission verses percentof clockwise (FIG. 9) and counterclockwise (FIG. 10) rotation of theguidewire 10 is illustrated in comparison with two prior art guidewireconstructions. The ordinate axis illustrates the normalized energytransmission from the proximal end of a guidewire 10 to the distal tip14. Perfect transmission has a value of unity, that is no storage ofapplied energy in the guidewire itself. The abscissa shows rotation ofthe proximal end of the guidewire as a percentage of 360° (thus, 20%rotation is 720). Curve A is of a guidewire 10 according to theinvention in which the fiber section 24 is fixedly attached to thetubular section 22. Curve B is of the Rowland et al. guidewire. Curve Cis of the Geenan guidewire. FIGS. 9 and 10 illustrate that the inventiveguidewire 10, provides enhanced torque transmission as compared to knownERCP guidewires. The improvement over known designs is directlyattributable to the use of tubular section 22 instead of a solid core ofNitinol.

In addition, it has been empirically observed that a generally rigidtubular element can elastically contain stress (by deforming to an ovalcross-section) as the guidewire 10 is advanced through bends in apassageway, and is therefore more flexible than a solid core stainlesssteel construction, yet transmits more torque than a highly flexibleguidewire formed entirely from a superelastic alloy as demonstrated inFIGS. 9 and 10. Further, hypotubes are less prone to kinks than solidcore constructions of similar outer diameter, and provide a simpleattachment to a more proximal segment such as the fiber section 24.

The tubular section 22 is coated or sprayed with a layer of polyimide,polytetrafluoroethylene (Teflon), fluorinated ethylene propylene (FEP),or other material, to provide electrical insulation to this portion ofthe guidewire 10 and reduce the friction of the outer surface of theguidewire. This layer may be about 0.25 mil to about 1.0 mil thickexcept perhaps along its most proximal 12 cm where the coating may bethinner or absent for attachment of the vice 16.

The distal segment 19 and the tubular section 22 may be further jacketedin a hydrophilic coating 44 (FIG. 1) such as polyurethane, polyethylene,polyimide, fluoropolymer, or a combination of these materials. A furtherdescription of hydrophilic and hydrogel coatings can be found in U.S.Pat. Nos. 5,077,352; 5,179,174; 5,160,790; 5,290,585, all of RichardElton and assigned to the present assignee, the disclosures of which arehereby incorporated by reference as if set forth in their entiretyherein. This hydrophilic coating is secured directly to the outermostsurface of the guidewire 10 (including the Nitinol rod 20, sleeve 36,hypotube 22 and perhaps the fiber core 24) to provide a low coefficientof friction.

As illustrated in the cross-section of FIG. 8, the fiber section 24 ispreferably a glass/epoxy composite comprising a multiplicity of glassfibers 46 10-15 microns in diameter, preferably 12-14 microns indiameter. Known fibers 46 that can be used in place of glass includearamid (Kevlar), oriented polyolefin (Spectra), and any elongate elementwhich has an overall flex modulus of at least four million pounds persquare inch ("psi"), preferably at least seven million psi. Theforegoing are illustrative (and not restrictive) of the types ofelongate elements that can be used as fibers 46 to form the fibersection 24.

The fibers 46 are encapsulated in an epoxy or polyester thermoset resin48. The resin 48 encapsulation layer is preferably about 25.4 to about50.8 microns (about one to about two mils). The resin 48 contributes tothe hoop strength of the guidewire 10 and increases the minimum bendradius that the fiber section 24 can withstand without breakage. Onesuitable glass/epoxy composite is manufactured by Neptco, Inc. ofPawtucket, R.I., and is sold under the trademark LIGHTLINE. TheLIGHTLINE glass/epoxy composite includes 1600 fibers in cross-section.The fiber section 24 including fibers 46 and resin 48 preferably has anominal diameter of about 400 to about 700 microns (about 20 to about 30mils).

In the illustrated embodiment, a sheath 50 envelopes the fiber section24 and is bonded thereto. The sheath 50 is preferably plastic, and maybe made from fluorinated ethene propene (FEP), polytetrafluoroethylene(TFE), pefluoroalkoxy resin (PFA), chlorinated triflouroethylene (CTFE),polyolef in, polyurethane, polyether amide block copolymer, or the like.The sheath 50 permits the guidewire 10 to bend to a smaller radius witha reduced likelihood of guidewire breakage during storage because itpermits the guidewire 10 to be dispensed from a coiled hoop of smallradius. The sheath surrounds at least the entire fiber section 24 toprovide a generally smooth outer surface to that section of theguidewire 10.

In operation, the guidewire 10 is initially advanced through a lumen ofan ERCP cannula, papillotome or other catheter used in the ERCPprocedure. The vice 16 is selectively secured at an appropriate pointalong the proximal end of the tubular section 22 to assist in steering(torquing) the guidewire 10 until the guidewire exits the distal end ofthe ERCP catheter 11. Once the guidewire 10 has been positioned, asconfirmed by fluoroscopic imaging of the area, a catheter 11 can beadvanced to the major or minor papilla of Vater, pancreatic or commonbile duct, cystic duct, right or left hepatic duct, etc. to perform therequired procedure. If a catheter exchange becomes necessary, it can beperformed without axially displacing the guidewire 10 by withdrawing thecatheter over the fiber section 24, which is either permanently attachedto the proximal end of the tubular section 22 or selectively attachedfor permitting the catheter exchange procedure.

As will be readily apparent to those skilled in the art the dimensionsstated relate to one particular guidewire size and are disclosed solelyby way of example and should not, therefore, be understood as anintended limitation on the scope of the invention.

It is preferred that the Nitinol have the temperature at which itstransformation to austenite is complete be between about 15° C. and 21°C. to ensure that the material is superelastic at the temperatures atwhich the guidewire 10 is expected to be used.

Having thus described a preferred embodiment of the present invention,it is to be understood that the above described device is merelyillustrative of the principles of the present invention, and that otherdevices may be devised by those skilled in the art without departingfrom the spirit and scope of the invention as claimed below.

I claim:
 1. A guidewire for use in endoscopic retrograde cholangiopancreatography (ERCP), comprising:a proximal section comprising a fiberrod, a tube, and means for attaching the tube and fiber rod together ina collinear relationship, a flexible distal section, said distal sectionbeing attached to the distal end of the tube and comprising(i) asuperelastic core having a proximal end of a first diameter and a distalend of a diameter no greater than that of said superelastic core wireproximal end, and (ii) a radiopaque marker disposed about the distal endof said superelastic core; and an insulative sleeve enveloping at leasta portion of said distal section.
 2. The ERCP guidewire as in claim 1,wherein said superelastic core is tapered.
 3. The ERCP guidewire as inclaim 2, wherein said radiopaque marker is a coil which is tapered tomatch the taper of said superelastic core.
 4. The ERCP guidewire as inclaim 1, wherein the stiffness of said sleeve progressively decreasestoward the distal end of the guidewire.
 5. The ERCP guidewire as inclaim 1, in which said fiber rod comprises a multiplicity of fibersselected from the group consisting of glass, aramid and polyolefin,encapsulated in a material selected from the group consisting of epoxyand polyester thermoset resin.
 6. The ERCP guidewire as in claim 5wherein a plastic sleeve is bonded to the fiber core.
 7. The ERCPguidewire as in claim 1, wherein the tube has a non-circular portionwhich defines an engagement surface to facilitate the application oftorque to the guidewire.
 8. A guidewire for use in endoscopic retrogradecholangio pancreatography (ERCP), comprisinga proximal sectioncomprising a fiberglass rod, a hypotube, and means for attaching thehypotube and fiberglass rod together in a collinear relationship, aflexible distal section, said distal section being attached to thedistal end of the hypotube and comprising(i) a Nitinol core having itsdistal end tapered, and (ii) a radiopaque coil secured to the tapereddistal end of said Nitinol core; and an insulative sleeve enveloping atleast a portion of said distal section.
 9. The ERCP guidewire as inclaim 8 wherein said coil is tapered to match the taper of said Nitinolcore.
 10. The ERCP guidewire as in claim 8, wherein the stiffness ofsaid sleeve progressively decreases toward the distal end of theguidewire.
 11. The ERCP guidewire as in claim 8, in which saidfiberglass rod comprises a multiplicity of fibers selected from thegroup consisting of glass, aramid and polyolefin, encapsulated in amaterial selected from the group consisting of epoxy and polyesterthermoset resin.
 12. The ERCP guidewire as in claim 11, wherein aplastic sleeve is bonded to the fiberglass core.
 13. The ERCP guidewireas in claim 8, wherein the tube has a non-circular portion which definesan engagement surface to facilitate the application of torque to theguidewire.